Movie itself is supposed to lead into Captain America 3, which (duh) kicks off Civil War and the third phase. Trailer really hammers that home, I thought, as Tony's regret over what he's built and contributed to Avengers and superheroes in general comes across pretty clearly, thus setting him up to go in for registration.
CA3 is supposed to be Downey's last turn as Iron Man, which, storyline-wise would likely be due to him refusing to put on the armor anymore (as mentioned and leading into and through that).
Evans' contract runs out at that point, too, so it's supposed to be highly likely that Marvel turns to the Winter Soldier taking up the shield storyline, at that point, and it will be interesting to see if they focus almost entirely on newer characters (Ant Man is coming soon, the various others that play important parts in CW), or if they try more with the rebooted (basically) old guys (new Iron Man, maybe she-Thor since Helmsworth may be too expensive to bring back, don't forget that Marvel Studios is legendarily cheap).
edit: can't wait to see Vision in (hopefully) the next trailer.